Filing Code 7200
Date Issued January 1975
U.S. DEPARTMENT OF THE INTERIOR - BUREAU OF LAND MANAGEMENT
PROPER LOCATIONS FOR
STORAGE PRECIPITATION GAGES
David W. Moore
Vernal District, Utah
Additional copies of Technical Notes are available from DSC, Federal Center Building 50, Denver, Colo., 80225
The proper location of precipitation gages will improve the reliability
of rainfall records and management decisions.
Most BLM districts maintain a network of storage precipitation gages.
Many of these have been in operation for 15 or more years. If the gages
were not properly placed when installed, records can be in error as
much as 25 per cent.
To improve the reliability of precipitation information, gage locations
should be reviewed for adequate placement. If found to be in poor
locations, gages should be moved to better sites. However, when a gage
is relocated, its past record should be retained for possible future
adjustment based on data at the new location.
The following guidelines can be used to improve the accuracy of precip-
1. Avoid bare ridges and benches. (Figure 1)
2. Where possible, use Pinyon Juniper, large shrubs, or
similar vegetation as a wind shield. This can be done
by using the following rules:
Starting at the top of the container, measure up and
out at a 45° angle. All vegetation should fall out-
side the imaginary cone. (Figure 2)
A better rule, when possible, is to be sure that the
distance from the shielding vegetation to the gage is
equal to at least twice the height of the vegetation.
3. When a gage must be placed in an area of tall trees
(> 50 feet), a clearing should be used that has a minimum
diameter of 50 feet. (Figure 3)
4. Small canyons and draws are better than no protection
at all, but should be avoided if possible. (Figure 4)
5. If none of the above is available, a commercial wind
shield should be considered for the gage. (Figure 5)
If the above suggestions are followed, precipitation information will
be accurate and of greater value in BLM management decisions.
4-flC •**,.» QX*& ^e*
*n A0> , ~«sl 2P ,.o 9,5" w
Figure 1. Avoid unprotected areas,
Figure 2. The cone above the gage should not be obstructed.
i \ i
Figure 2a. When possible, the distance between gage and shielding
vegetation should be twice the height of the vegetation.
,:■ ■/ ."" a Jb
Figure 3. The opening in the trees should be at least 50 feet wide.
Figure 4. Even a little protection helps.
Figure 5. A commercially built wind shield can take the place of natural
GPO 857 - 962
^.;: ; v,-
• ■_ ■
D-553A, Building 50
Denver Federal Center
P.O. Box 25047
Denver, CO 80225-0047